Analysis of a series of M(SR) 4n- complexes to understand the relationship of Cl to S K-edge XAS and develop a comparable sulfur based approach to study electronic structure and bonding. The methodology of the S K-edges will then be applied to a series of multi-nuclear Fe-S centers in model complexes and proteins also to heterometal systems containing M-Fe-S moieties similar to those of nitrogenase. These studies will be used to understand covalency and electronic structure of bioinorganic systems such as blue copper, iron sulfur, and heterometal cluster-containing proteins.